This invention relates to industrial platforms and in particular to plastic pallets with improved features and characteristics preferably constructed according to triple sheet thermoforming methods.
Wooden stringer pallets are the preferred materials of pallet construction within the North American distribution system. Four hundred (400) million new or refurbished wooden pallets are introduced into a distribution system comprising 1.9 billion pallets each year, according to the US Forest Service.
Plastic pallets have been used to replace wood pallets with some degree of success over the past several years. Plastic pallets have a low market share however because they suffer from one significant disadvantage in that they are considerably more expensive than a comparable wooden pallet. Thermoplastic materials constitute a significant proportion of the total cost of a plastic pallet, and a given amount of relatively expensive plastic material is required to produce a pallet with a measure of load-bearing strength that is comparable to wooden pallets. Therefore, the plastics industry is attempting to overcome the initial price difference that exists between wooden and plastic pallets, so that the plastics industries can gain more market share.
Approximately 4 to 6 percent of the annual North American production of pallets are in the form of plastic pallets. Increasing the strength while utilizing less material is an important object of the plastics industry. The plastic industry however has reached a plateau. Only marginal, rather than significant break through in increased strength to weight ratios have been anticipated using conventional methods of the plastics industry.
The twin sheet thermoforming sector of the plastics industry has captured a share of the plastic pallet market disproportionate to its share of the overall plastics industry. Accordingly, it may be suggested that the art of thermoforming is a competitively and comparatively advantageous starting point for the development of new break through plastic pallet methodologies.
The xe2x80x9cstandardxe2x80x9d 48xc3x9740-inch wooden stringer pallet has a dynamic load bearing performance specification of 2,800 pounds. This load bearing specification is the benchmark against which plastic pallets are compared. In order to meet this specification in thermoformed plastic, a combination of two (xc3x972) twin sheet pallet members have been proposed. Two twin sheet members are combined to provide what in known in the material handling industry as a rackable plastic pallet.
Conventional rackable twin sheet pallet designs comprise a load supporting platform and a load-distributing base. Three common techniques are used by thermoforming practitioners to join the load supporting platform and the load distributing base in a fixed spaced apart relationship for the introduction of fork lift tines and the like for movement and storage of the plastic pallet within the distribution system. A first method characterized in U.S. Pat. No. 5,413,052 to Breezer et al., utilizes a plurality of separately molded blocks to maintain the twin sheet members forming the deck and the base of the pallet a fixed distance apart. A second method characterized in U.S. Pat. No. 5,117,762 to Shuert suggests a load supporting platform with a plurality of depending legs to maintain the twin sheet pallet members a fixed distance apart. In yet another method, two pallet members are fused together where corresponding mirror image projecting elements upon each member come together, as in U.S. Pat. No. 5,401,347 to Shuert. Each method characterized presents problems. In the first methodology, an undesirable plurality of mechanical fasteners and molded elements are required. In the second method, the load-bearing surface of the platform has pockets forming the leg projections, which reduces the surface area available for supporting a load. In the third method, where the two members are fused together, the arrangement is disadvantageously permanent. These approaches are not satisfactory. A low cost means of coupling and de-coupling the members of a racking style pallet is needed.
In order to meet the 2,800-pound load bearing benchmark it has also been necessary to encapsulate metal frame structures between the twin sheets comprising the thermoformed pallet members. U.S. Pat. No. 5,404,829 to Shuert illustrates in FIG. 7 how the top sheet of thermoplastic forming the load support deck includes elements that depend downward from the surface to capture reinforcing beams. In the U.S. Pat. No. 5,413,052 execution of a reinforced pallet no depending elements on the load-bearing surface are suggested. A substantially uninterrupted surface is preferred over a relatively stronger developed surface having several pockets or depressions. The deck member of ""052 would however be unsatisfactory for supporting loads without the reinforcing cross members because this structure would be considerably weaker than a deck with a developed surface structure. Accordingly, a mold combination that can produce either a strong non-reinforced or an exceptionally strong reinforced pallet without interruptions on the load-supporting surface would be advantageous and is therefor needed.
Plastic pallets must also provide a level of fire resistance that is at least equal to or better than wooden pallets should a fire occur within the warehouse setting. Plastic pallets will not substitute wooden pallets on a large scale if plastic pallets create hazards that prevent a fire from being extinguished. A plastic pallet that creates more fire hazards than a wooden pallet will necessitate fire protection upgrades, including increased sprinkler systems and insurance premiums that could become very costly to the plastic pallet user. According to this problem, one pallet known as the GE Extreme(trademark) Pallet has been offered. The GE Extreme(trademark) Pallet is UL classified and Factory Mutual approved to meet the National Fire Code (NFPA 13) for commodity and idle storage of pallets. Although this particular plastic pallet has been used to some advantage, it is nonetheless heavy weight (approx. 57.5 pounds) and is constructed of plastic materials made from expensive General Electric Company Noryl(copyright) and Xenoy(copyright) resins. The problem is that these resins are considerably more expensive than the commodity resins of the olefin group such as polyethylene and polypropylene, which are the preferred materials for constructing low cost plastic pallets.
A number of methodologies have been used in the past to provide fire retardant polyolefin compositions, as for example in electrical wiring. These prior art methods may be known by referring to U.S. Pat. No. 3,810,862 to Mathis et al, U.S. Pat. No. 5,356,983 to Vijayendran et al. and U.S. Pat. No. 5,946,878 to Grund et al. A first problem with these methods is that the materials are relatively expensive as they are used throughout the article""s resinous composition. A second problem is the resultant loss of the physical properties and general processability of the carrier resin forming the article.
Coatings have also been proposed to provide protective fire retardant properties to plastic structural articles, and may be understood by referring to U.S. Pat. No. 5,924,589 to Gordon and U.S. Pat. No. 6,110,559 to De Keyser. An intumescent coating system comprising a first layer providing a breakthrough barrier and a second layer providing thermal insulation has also been proposed, as in U.S. Pat. No. 5,989,706 to McGinniss et al. Problems with coating systems are that they require secondary manufacturing operations and materials which can be expensive to acquire and apply and they would be subject to damage/removal in a rough pallet handling environment.
It is known that thermoformable resins can be co-extruded to yield an engineered sheet construction with enhanced characteristics. For example, U.S. Pat. No. 5,143,778 to Shuert proposes a co-ex sheet construction to provide a more rigid pallet structure. The co-ex principle has been suggested by Gordon in U.S. Pat. No. 5,984,126 to provide an industrial container formed from a structural sheet that has an outer layer of fire resistant intumescent material to prevent the breaching and subsequent spilling of flammable lading. Although the Gordon approach may be useful in some applications, it would be difficult to implement the approach in a twin sheet pallet that would typically be under load. Polyolefins have a notoriously low heat deflection temperature and a co-ex intumescent twin sheet pallet construction would surely collapse when softened by the heat of a fire. It is also not known what intumescent admixture Gordon proposes. Another problem being that an intumescent system must be processable by the practitioner of thermoforming methods. According to these problems, a new and useful approach is needed to provide a fire resistant pallet that will also maintain it load bearing strength in high temperature environments.
It may also be appreciated that conventional wooden pallets are low-tech. Plastic pallets are becoming increasingly sophisticated. A hollow pallet having an internal wireless communications devise that triggers a 911 emergency data signal in response to a fire or the heat of a combustion flame to a remote xe2x80x9cemergencyxe2x80x9d monitor would be beneficial.
It is also understood that plastic pallets have been used to replace wooden pallets with some success because wooden pallets deteriorate through normal wear and tear. Examples of wooden pallet deterioration include, but are not limited to, splintered wooden boards and stringers and projecting nails. In addition to causing damage to packaging materials and automated pallet handling equipment, these examples of deterioration also cause workforce injuries as a result of manual wooden pallet handling. While plastic pallets eliminate these problems to a large extent and have been used to some advantage because they do not deteriorate in the same fashion, it may be argued that plastic pallets remain nonetheless difficult to manually handle by warehouse workers because of their heavyweight construction. Pallets in the prior art have not been developed with ergonomic principles in mind. Ergonomic pallets are needed.
It is also known that plastic pallets, which are used to support loads that may be suspended upon racks adjacent the work area of a warehouse worker, are often times constructed of plastic materials that exhibit low coefficients of friction. Two such materials with relatively low coefficients of friction include polyethylene and polypropylene. According to this potential safety problem it has been advantageous to offer such pallet materials with skid resistant properties or treatment. For example, in U.S. Pat. No. 4,428,306, a non-skid surface is applied to the polyethylene sheet prior to forming the pallet structure. Alternatively, in U.S. Pat. No. 5,648,031, it has been suggested anti-slip droplets may be sprayed upon the surface of the material forming the plastic pallet to provide a skid-resistant treatment. Although these and other approaches provide some skid resistant protection they are disadvantageous in that they required additional material and or processing expense in their original manufacture and eventual recycling. Pallets with a high coefficient of friction surface on the top and the bottom are needed to prevent slippage of the load carried by the pallet, and slippage of the pallet on the support surface.
It is also known that plastic pallets must interface within distribution networks where it is common to unitize a pallet load with shrink-wrap and other banding materials. Plastic pallets have not been adequately developed to interface with these and other packaging methods. In U.S. Pat. No. 5,676,064 to Shuert, a downward extending peripheral lip and indents in the outer leg structures are suggested to accommodate packaging materials. Similarly, in U.S. Pat. No. 5,408,937 to Knight, et al., indented surfaces upon the legs are suggested to receive wrapping materials. Although these arrangements are helpful, they do not allow the warehouse worker to manually and ergonomically initiate the starting stretch and cling of widely used packaging films around the pallet for final unitization. A pallet amenable to unitization is needed.
Regarding the foregoing, it is understood that plastic and in particular thermoformed plastic pallets have many advantages over wooden pallets. These advantages are properly recorded in the prior art. The disadvantage of initial price, however is increasingly a more complex justification for selecting wooden pallets when these are compared to plastic pallets. Although twin sheet plastic pallets have been employed successfully to replace wood, breakthroughs in the cost equation and the value-added execution of thermoformed plastic pallets are finally needed to justify a wholesale conversion from wooden pallets to plastic pallets.
It is therefore an object of this invention to provide a comparably stronger industrial platform than has heretofore been possible using conventional thermoforming methods.
According to this object, pallet structures with higher load bearing strength are offered using a triple sheet thermoforming methodology. According to this methodology, triple sheet pallets using the same measure of plastic as in a twin sheet pallet are significantly stronger than twin sheet pallets.
It is also an object of this invention to offer a triple sheet pallet, while using less material, which is equal in strength to a twin sheet pallet. According to this aspect, the plastic forming the triple sheet pallet is extruded in a thinner over-all gauge to reduce costs. The relatively thinner sheets of plastic are therefore specially developed for triple sheet thermoforming. Three molded sheets can provide the same load bearing strength as two molded sheets, even though the combined weight of the three sheets is significantly lower than the combined weight of the two sheets. According to this aspect triple sheet pallets, using a much lower measure of plastic, provide the same load bearing strength as significantly heavier and therefore costlier twin sheet pallets.
Other objects of the present invention are offered below. The present executions of triple sheet thermoformed pallets embodied herein are not presented as being definitive but rather as exemplary of the improvements and advantages that are attendant when executing a plastic pallet in a thermoforming methodology. Many embodiments of the present triple sheet pallet may also be used in twin sheet pallets.
Another object is to provide heat deformable plastic with improved hot tack adhesion characteristics for increased bond strength. A thinner or lower over-all measure of plastic can be used successfully if the sheet construction is amenable to improved hot tack adhesion. A means of scuffing the surface of the sheet, as it is extruded prior to thermoforming, is disclosed. One or both surfaces of the sheet material suggested for use in a pallet can be scuffed selectively to increase sheet-to-sheet bond strength.
It is an objective to be able to selectively join and un-join the members forming a pallet in order to increase their efficiencies of use. It is therefore suggested that the sheets forming the pallet members include interfacing clasping features. A xe2x80x9csnap together and snap apartxe2x80x9d feature is provided. According this aspect, the feet of the load-supporting platform include protrusions that are received in recessions formed in the load-distributing base. Two pallet members are joined by a snap fit to provide a rackable pallet. A snap together, snap a-part improvement will allow the pool of pallet members to be more effectively marshaled, and thus reduced in over-all number, according to asset management principles.
Another objective is to develop the three molds deforming the plastic sheet to accept rigidifying cross members without modification (such as the replacement of loose pieces or substitute molds). In this manner a non-reinforced pallet member may be replaced with a reinforced pallet member in response to demand fluctuation and changing customer requirements. When the non-reinforced pallet member is formed in the triple sheet manufacturing process, the details otherwise receiving the cross members mold over or web together providing structural strength when an insert is not offered. Accordingly one mold group may be employed to produce either a rigid non-reinforced pallet member or a substantially more rigid reinforced pallet member. When metal reinforcements are preferred, these may be placed advantageously between the first and the second, or the second and the third sheet formed in the triple sheet thermoforming sequence to yield a heavy-duty reinforced pallet structure.
Another object is to offer a plastic pallet that is as much as or less than a fire hazard as wooden pallets. According to this object, the sheet forming the thermoformed pallet is developed to provide a fire resistant barrier that is more fire resistant than wood. According to this aspect, an intumescent polymeric material is co-extruded over the polyolefin resins, such as polyethylene or polypropylene forming the core substrates of the top and bottom sheets comprising the thermoformed pallet. According to this aspect only a relatively small amount of comparably expensive intumescent polymeric material is used to provide a fire resistant plastic pallet. The use of a smaller measure of expensive fire resistant material as a protective fire retardant surface is more economically advantageous than producing the entire pallet with such expensive fire resistant materials as has been provided for in the past by the aforementioned examples. In accordance with this objective, an intumescent system that has good thermoforming processability is also provided. In further accordance with this object, the intumescent system provided also has excellent thermal insulating properties, which properties are preferred so that the interior structural sheet of the triple sheet pallet is protected against the heat that is generated by the high temperature of the combustion flame. By preventing the interior structural sheet from softening upon exposure to heat the pallet will be able to maintain its load carrying properties even while the outer sheets exposed to flame decompose through intumescent efficiency. Accordingly, it is will be further understood why a triple sheet pallet with a central structural member is superior to a conventional twin sheet pallet in which only two exposed sheets are developed to provide load bearing strength. In further accordance with this objective, the cross members that may be inserted within the core of the pallet to provide additional load bearing strength may also be provided with intumescent properties to decrease their thermal conductivity within the pallet structure. These arrangements will help to protect fire fighters working adjacent pallet loads suspended in idle storage upon warehouse racks during a fire and should help reduce the damaging consequences of a fire by maintaining the stored articles upon the pallets.
Another object includes a wireless communications devise within the plastic pallet that responds to a fire or the high heat of a fire by triggering an emergency 911 data transmission to a remote monitoring location. Such adaptations to the wireless communications devise would be contemplated in connection with the principles and equipment disclosed by the present inventor""s co-pending U.S. patent application entitled xe2x80x9cThermoformed Apparatus having a Communications Device,xe2x80x9d filed Jan 24, 2000, which is incorporated hereunder in its entirety by such reference.
Another object is to provide handles adjacent the perimeter of the plastic pallet so warehouse workers can manually handle the plastic pallets with less chance of injury. According to this aspect, a pair of handles are provided along the margin of the pallet and the plastic pallet base is provided with a skid plate along its leading edge opposite the handles to increase the pallet""s resistance to wear through abrasion cause by pallet dragging.
Another object is to provide a plastic pallet with surfaces having high coefficients of friction so that cargo carried by the pallet does not easily shift or dislodge to injure a warehouse worker. According to this object, the sheet surfaces comprising the pallet are scuffed during the extrusion process to provide a skid resistant surface that does not add material or processing cost and is 100 percent recyclable.
Still another objective is to provide a means for securing a variety of packaging materials to the members forming the plastic pallet. The four corner zones of the load carrying deck may be developed to receive a knot of shrink-wrap material so that a dispensing roll may be manually employed satisfactorily by the warehouse worker. The opposing peripheral edges between the four corners of the pallet may include selectively located depending structures that are amenable to receiving stretch wrap, banding, straps and the like. A saw tooth or a serrated boarder configuration positioned between the leg pockets may be provided to engage a plurality of different packaging elements for their economical deployment by a warehouse worker.
These and other objectives, improvements and features will be in part apparent and in part pointed out in the drawings provided, the detailed descriptions given and hereinafter the appended claims.